The present invention is directed to a method and apparatus for the inventory and management and automated discharge of treated sewage sludge to trucks, and includes inventory management by tracking the flow of sludge from bins to trucks on a first-in/first-out basis, automated truck positioning, automated precision truck loading and an operating system program for monitoring and controlling all of the interrelated components.
In the treatment of sewage sludge so that it can meet the various criteria of the U.S. Environmental Protection Agency, so that the sewage sludge can be returned to the earth as fertilizer, or in some cases be used as ground fill, it has become commonplace that the sludge is first treated to remove pathogens, or at least reduce the pathogens in the sludge to an EPA acceptable level and to reduce the attractiveness of the sludge to vectors such as rats, mice, flies, etc., as well as to reduce the odors that may otherwise emanate from the sludge. In some cases, the treatment to kill pathogens is by heating the sludge to a high temperature for a period of time. In other cases, the sludge is treated by a process of pasteurization to neutralize pathogens and to reduce vector attractiveness. Often, both heat and pasteurization are employed. In many cases, the treatment involves lime stabilization, to elevate the pH of the sludge to a sufficient degree for a pre-determined period of time. Such a treatment often involves the addition of an alkaline substance such as calcium oxide, calcium carbonate and/or compounds such as quicklime, lime kiln dust, cement kiln dust or dolomitic lime. The sludge generally has both solid and liquid components. Often, the sludge is dewatered to produce a higher solids content. The solids content of the sludge can vary, such that the physical characteristics of the sludge can range from a viscous, colloidal liquid to a dry cake or clay-like texture.
Some of the methods and apparatus for treating sludge, to which the present invention is addressed in terms of an automated discharge of treated sewage sludge into trucks include the following patents, all of which are herein incorporated by reference:
5,013,4585,186,8405,229,0115,346,6165,401,4025,405,5365,433,8445,554,2795,618,4425,681,4815,783,0735,851,4047,669,3487,416,673
In accordance with the present invention, dewatered sludge is delivered to a conveyor device that can be any of various types, such as a belt conveyor, a screw conveyor, a pump for pumping sludge through a duct or tube, or any other conveyor devices that supplies sludge to a gravity flow bin. Preferably, a plurality of conveying devices are used, each supplying sludge to a different gravity flow bin. One such apparatus for delivering dewatered sludge to a conveyor mechanism for, in turn, delivering sludge to one or more gravity flow bins, is disclosed in U.S. Pat. No. 6,447,674, the complete disclosure of which is herein incorporated by reference.
Generally, dewatered biosolids (sludges) have, by their nature, a resistance to flow because water has been removed and flocculants, generally of polymeric material have been added to thicken the sludge by adsorbing onto sludge particles to aggregate the sludge particles. During the treatment of the sludge, calcium has been added to the sludge to reduce pathogens, and the polymeric material has also been added to the sludge in order to provide flocculation. By adding a flocculant, the sludge develops a consistency similar to that of cottage cheese, and then the sludge is squeezed to reach a semi-solid appearance, having about 20% solids, with the rest being water.
In some cases, simply opening a bottom gate of the flow bin is enough to initiate flow, as gravity takes over. In other cases, the resistance to flow and/or the wall friction exceeds the force of gravity, particularly when the quantity of sludge in the flow bin is reduced, thereby reducing the “head” of sludge in the bin. When gravity flow bins are fully loaded, there is a greater amount of “head”, facilitating the unloading of the bin when the bottom gate is opened. However, if the bin is only slightly full, the sludge may have formed as “cake”, perhaps having remained in the bin for a couple of days without any sludge having been removed from the bin in that period, and gravity flow may not as easily occur.